Hydraulic power transmission for overrunning load



April 17, 1956 J. P. HORVATH 2,741,895

HYDRAULIC POWER TRANSMISSION FOR OVERRUNNING LOAD Filed April 24, 1955 INVENTOR. JOSEPH P. HORVATH ATTORNEY United States ParentO HYDRAULIC POWER TRANSMISSION FOR OVERRUNNING LOAD Joseph P. Horvath, Detroit, Mich, assignor to Viclrers Incorporated, Detroit, Mich., a corporation of Michigan M Application April 24, 1953, Serial No. 350,848

8 Claims. (Cl. 60-53) systems a fluid motor is customarily provided in a driving.

relation with the load, and a fluid pump is utilized as a source'of pressure to operate the motor. To effect the selective starting and stopping of the load and the motor, and in the case of a double-acting motor to provide for reversing the motor and load, there is ordinarily provided a directional valve to efiect the interruption of, or establish, communication between the fluid pump and the motor. i

' Customarily, such valves are of the type wherein the relation of the valve lands and the motor ports controlled thereby is such that as the land crosses the' po'rt the port is momentarily blocked-by the land. Such an arrangement provides a valve position in which the motor ports are blocked to permit locking the motor in a desired position. Further, the slight overlap of the land prevents the motor portfrom acting as a fluid path to short circuit the pump across the valve lands.

The use of such avalve in asystem utilized for driving a load with a heavy inertia moment has an inherent disadvantage in that surgeor transientpressures ofmaggenerated. For example, assume that a double acting fluid motor is driving an inertia load at a substantial rate of;

speed with the valve connecting the pump outlet to one of the motor ports and connecting the other motor port to tank. If the valve is suddenly shifted to a position wherein the motor port serving to return fluid to the reservoir is blocked, the pressure generated in the blocked motor line by the motor being driven as a pump by the inertia load may be extremely high. For example, in a particular transmission of this type, where the pump op erating pressure was 3000 p. s. i., pressures generated by the overrunning of the inertia load were measured to be of the order of 15,000 p. s. i. Pressures of such magnitude are destructive of system components and might run even higher, dependent on the kinetic energy storedin the moving load, and the rate of deceleration.

In the past, systems have been guarded against damage due to such transient pressures by the provision of a relief valve in the linebetween thedirectional valve and the motor. The relief valves provided in the past have been of the conventional type wherein the fluid discharged to relieve excess pressure is discharged directly to the'reservoir. Such an arrangement has several serious disadvantages. .One of these disadvantages is that, since the valves must not open under normal system pressures, which may be of the order of 3000p. s. i., extremely heavy biasing means must be utilizedto maintain the valve in a closed position. Utilization of such a valve 2,741,895 Patented Apr. 17, 1956 ice results in inaccurate operation and the necessity of heavy general construction of the valve.

It has also been proposed to use a relief valve of th hydracone type wherein a small pilot valve effects operation of a large main valve. permits use of a relatively light control spring due to the small area of the pilot valve, but has the disadvantage of introducing to the system a relatively large body of oil which adversely afiects the response characteristics of servo systems in which positional and speed control are critical.

It is an object of this invention to provide a power transmission for driving an inertia load in which the system components areadequately protected against excessive pressures caused by overrunning of the load.

Further, it is an object of this invention to provide, in such a system, valves for relieving the inertia produced pressures, which valves are operative only at very high pressures and yet which may utilize extremely light mechanical biasing means.

Still another object is to provide such a system in which inertia induced pressures are properly relieved, and in which the mass of oil in the system between the directional valve and the motor is kept to a minimum.

A still further object is to provide such a system in p which simple, low cost components are used in which piping connections are simple and few in number.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing wherein a preferred form of the present invention is clearly shown.

In the drawing:

The single figure is a schematic view of a power transmission employing a preferred form of the present invention.

There is illustrated in the drawing a pump 10 of the axial piston type having a drive shaft 12 for connection to a prime mover, not shown. Connected to the pump 10 by fluid conduits hereinafter described is a fluid motor 14, also being illustrated as of the axial piston type. The motor 14 is connected by a drive shaft 16 to a load having a large moment of inertia and indicated at 18.

The system includes a reservoir 20 which provides a supply of fluid to replenish leakage and also provides a point of relative quiesence in the system where the operating fluid is cooled, deaerated, and cleaned. A suction conduit 22 leads from the reservoir 20 to the inlet port of the pump 10. Fluid pumped by pump 10 is discharged therefrom through the delivery conduit 24 which leads to the inlet of a relief valve 26. The delivery conduit 24 extends fromthe other side of relief valve 26 to the inlet port 28 of a directional valve generally designated 30. Valve 30 includes operating mechanism 31 which may be connected to any suitable source of a control input.

An exhaust conduit 32 extends from the relief valve 26 to the reservoir 20, and operation of the valve 26 is such that fluid is diverted from the conduit 24 to the discharge conduit 32 and hence to tank 20 in such quantities as are required to maintain the maximum delivery pressure of the pump 10 at the pressure setting of the valve 26. a

The end chambers 34 and 36 of valve 30 are vented to the reservoir 20 through a branched passage 38 which leads from those end chambers to the discharge conduit 32. Thus while the pump 10 is in operation the central chamber 40 of valve 30 will be continuously under pump operating pressure conducted theretoby a delivery conduit 24; and each of the end chambers 34 and 36 will be maintained at reservoir pressure. The end chambers 34 and 36 are separated from the central chamber 40 by the lands 42 and 44 on thespool 46 "of the valve 30. The

This arrangement of course 3 lands 4'2 and 44 cooperate respectively with a pair of motorport's 48 and S in thebody of valve 31). The axial length of lands 42 and 44 preferably equals or slightly exceeds the axial extent of the ports 48 and 50 and the lands are spaced apart the same distance as are the ports.

It can be seen that with the valve spool 46 in the position indicated by the solid outline, the motor ports 48 and 50 will be blocked by the lands 42 and 44, and hence isolated from communication with both thecentral chamber 46 and the end chambers 34 and '36. Shifting the valve spool 46 to the position indicated by the dotted outlines will elfect fluid communication as indicated by the dotted arrows 52 and 54. Similarly, movement of the spool 46 to the position indicated by the alternate dot and dash outline will effect communication as indicated by the alternate dot and dash arrows 56 and 58.

Extending from the motor ports 48 and 50, respectively, are a pair of motor conduits 60 and 62 which lead to the motor 14. Motor '14is of the reversible type and capable of operation in either direction dependent on which of the conduits 6% or 62 is under pressure.

The conduits 60 and 62 have extending therefrom conduits 64 and 66, respectively. Conduit 64 leads to a spring biased ball type valve designated 68. Similarly, the conduit 66 leads to a valve of the same type, designated 70. Each of the valves, 68 and 70, comprises a housing having a central chamber 72 therein which contains a spring 74 and a ball '76. The spring 74 in each of the valves 68 and 70 biases the ball 76 therein to a position such that the central chamber 72 of the valve is isolated from its associated conduit 64 or 66. A branched passage 78 extends from the central chamber 40 of the valve 30 to communicate with the chamber 72 in each of the valves 68 and 70. As heretofore noted, chamber 40 is maintained at the outlet pressure of pump by a fluid conducted through the delivery conduit 24, and hence delivery pressure of pump 10 will be conducted to the chamber 72 of each of the valves 68 and 70. Each of the balls in the valves 68 and 70 is thus subjected on one side to pressure in the chamber 72 and on the other side to the pressure existing in the motor conduit 60 or 62 associated with that valve. Each of the balls 76 has exerted thereon a force due to its spring 74, a force due to the operating pressure of the pump acting upon the effective area of the ball exposed to pressure in chamber 72 and a force due to pressure in the motor line 60 or 62 associated with that valve and acting on the effective area exposed thereto. Since the effective areas of balls 76, which are exposed to operating pressure of the pump,

and pressure in the associated motor line are substantially equal, the pressure in the motor line must at least equal the pump operating pressure before the valve can be opened. Further, to open the valve the pressure in the motor line must exceed the operating pressure of the pump by an amount necessary to induce deflection of the spring 74. Any fluid passing through the valve 68 or 70 to relieve excessive pressure in the motor conduit 60 or 62 will result in increased discharge through the relief valve 26 which maintains the outlet pressure of the pump at the desired maximum.

In operation, the system relief valve 26 might be set to bypass fluid from delivery conduit 24 so as to prevent the operating pressure of the pump 10 from exceeding, say, 3000 p. s. i. Assuming that the valve spool 46 of the valve 30 has been moved to the position indicated by the dotted outline of the spool, fluid will flow through the conduit 24, through the central chamber 40 of valve 30, and through the valve port 50 into the motor conduit 62 leading the fluid motor 14. Rotation of motor 14 and inertia load 1-8 is thus induced. Fluid from the dis charge side of motor 14 passes through the motor conduit 60 to motor port 48, and from there passes through the end chamber 34 and the conduit 38 to the reservoir 26. l t should be noted that at this time full operating pressure of the pump 10 is imposed "on both the effective area of flow from the conduit 60 to the reservoir. As heretofore noted, the load 18 has a high moment of inertia and the blocking of motor port 48 tends to rapidly decelerate the motor 14, resulting in the creation of high pressure in conduit 60 which, if not relieved, would result in rupture of some of the system components.

With the valve spool 46 of the valve 30 in the position indicated by the solid outlines, the discharge of pump 10 is not being utilized and hence will be discharged over the relief valve 26 at its pressure setting of 3000 lbs. p. s. i. This 3000 lb. pressure also exists in chamber 72 of valve 68, and hence is exerted on ball 76 keeping valve 68 closed. A pressure in excess of 3000 lbs. p. s. i. will thus be required in the conduit 60 before the valve 68 will open. As heretofore noted, the amount by which pressure in the conduit 60 :mustexceed 3000 s. i. will be determined by the load of the spring 74. Assuming that the spring 74 is a. 500 p. s. -i. spring, that is, an unbalanced pressure of 500 p. s. i. is required on the area of ball 76 exposed to pressure in conduit 60 in order to open the valve; the valve 68 will relieve any pressure in conduit 60 in excess of 3500 lbs. lp. s. i.

When the motor 14 is operated in the reverse direction, analogous considerations are applicable to the operation of valve when the spool '46 of valve 30 is moved to the center position.

Thus by utilization of a relatively light spring of the order of 500 p. s. i-., the valves 68 and 70 will withstand 3500 p. s. i. before opening. Further, a very slight volume of oil has been added to that in the. conduits between the motor and valve to preserve satisfactory response characteristics of the system. Another important advantage derived from an arrangement such as that herein described, is that a minimum of piping connections is needed. For example, the fluid Which passes over the valves 68 and 70, in relieving surge pressures in the motor lines 60 and 62, is conducted to the reservoir through conduit 24 and conduit 32, which conduits are also utilized in the normal functioning of the circuit.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. In a power transmission for driving a load having substantial inertia, the combination of: a fluid pump; a fluid motor in a driving relation with said load; fluid supply and return conduit means interconnecting the pump and the motor; valve means in the supply and return conduit means to control fluid flow therein; means for preventing excessive pump operating pressure; and pressure responsive valve means having a pair of opposed effective areas, one of said areas exposed to pump operating pressure, the other to pressure in said return eonduit means between the first named valve means and the motor, said pressure responsive valve being normally closed but operative in response to pressure in said return conduit means to vent fluid from said return conduit means, whereby excessive pressures due to overrunning of the load are prevented.

2. In a power transmission for driving a load having substantial inertia, the combination of: a fluid pump; a fluid motor in a driving relation with said load; fluid supply and return conduit means interconnecting the pump and the motor; valve meansin the supply and return conduit means to control fluid flow therein; means for preventing excessive pump operating pressure; and pres sure responsive valve means having a pair of substantially equal opposed efiective areas, one of said areas exposed to pump operating pressure, the other to pressure in said return conduit means between the first named valve means and the motor, said pressure responsive valve being nor-- mally closed but operative in response to pressure in said return conduit means to vent fluid from said return conduit means, whereby generation of pressures substantially in excess of pump operating pressure due to overrunning of the load is prevented.

3. In a power transmission for driving a load having substantial inertia, the combination of: a fluid pump; a fluid motor in a driving relation-with said load; fluid supply and return conduit means interconnecting the pump and the motor; valve means in the supply and return conduit means to'control fluid flow therein; means for preventing excessive pump operating pressure; and pressure responsive valve means having a pair of opposed eifective areas, one of said areas exposed to pump operating pressure, the other to pressure in said return conduit means between the first named valve means and the motor, said pressure responsive valve means being spring biased to a normally closed position but operative in response to pressure in said return conduit means to vent fluid from said return conduit means, whereby excessive pressures due to overrunning of the load are prevented.

4. In a power transmission for driving a load having substantial inertia, the combination of: a fluid pump; a fluid motor in a driving relation with said load; fluid supply and return conduit means interconnecting the pump and the motor; valve means in the supply and return conduit means to control fluid flow therein; means for preventing excessive pump operating pressure; and pressure responsive valve means having a pair of substantially equal opposed effective areas, one of said areas exposed to pump operating pressure, the other to pressure in said return conduit means between the first named valve means and the motor, said pressure responsive valve means being spring biased to a normally closed position but operative in response to pressure in said return conduit means to vent fluid from said return conduit means, whereby pressure due to overrunning of the load is limited to an amount in excess of pump operating pressure determined by the load of said spring.

5. In a power transmission for driving a load having substantial inertia, the combination of: a fluid pump; a fluid motor in a driving relation with said load; fluid supply and return conduit means interconnecting the pump and the motor; valve means in the supply and return conduit means to control fluid flow therein; means for preventing excessive pump operating pressure; and pressure repsonsive valve means having a pair of opposed effective areas, one of said areas exposed to pump operating pressure, the other to pressure in said return conduit means between the first named valve means and the motor, said pressure responsive valve means being normally closed but operative in response to pressure in said return conduit to open fluid communication between that'part of the conduit means between the first named valve means and the motor and the pump outlet, whereby'excessive pressures due to overrunning of the load are prevented.

6. In a power transmission for driving a load having substantial inertia, the combination of: a fluid pump; a fluid motor in a driving relation with said load; relief valve means in communication with the outlet of the pump; fluid supply and return conduit means interconnecting the pump and the motor; valve means in the supply and return conduit means to control fluid flow therein; and pressure responsive valve means having a pair of opposed eflective areas, one of said areas exposed to pump operating pressure, the other to pressure in said return conduit means between the first named valve means and the motor, said pressure responsive valve means being normally closed but operative in response to pressure in said return conduit to open fluid communication be tween that part of the conduit means between the first named valve means and the motor, and the pump outlet, whereby excessive pressures due to overrunning of the load are prevented.

7. In a power transmission for driving a load having substantial inertia, the combination of: a fluid reservoir; a fluid pump; a double acting fluid motor in a driving relation with said load; a pair of motor conduits for conducting fluid to and from said motor; a pump delivery conduit; valve means for selectively connecting one of said motor conduits to the pump delivery conduit and the other to the reservoir; relief valve means communicating with the pump delivery conduit; and a pair of pressure responsive valve means each having an efiective area exposed to pressure in one of said motor conduits and an opposed efiective area exposed to pressure in said pump delivery conduit, said pressure responsive valve means being normally closed but operative in response to pressure in said motor conduit means to vent fluid therefrom to said pump delivery conduit, whereby excessive pressures due to over-running of the load are prevented.

8. In a power transmission for driving a load having substantial inertia, the combination of: a fluid pump; a fluid motor in a driving relation with said load; relief valve means in communication with the pump outlet; fluid supply and return conduit means interconnecting the pump and the motor; valve means in the supply and return conduit means to control fluid flow therein; secondary conduit means connecting the pump outlet to said fluid return conduit means between the valve and the motor; and check valve means in said secondary c0nduit, said check valve means being so oriented as to block flow from the pump, whereby excessive pressures due to overrunning of the load are prevented.

References Cited in the file of this patent UNITED STATES PATENTS 2,467,508 Trautman Apr. l9, 1949 

